## U th pb dating of phosphate minerals

thus, all of the evidence indicates that the observed age of ∼3. ga and that a disturbance to the u‐pb system occurred at ∼4. in this study, the younger age of 100 ± 130 ma recorded in eet 96008, which might be attributable to shock metamorphism [anand et al. u concentrations and 238u/206pb, 207pb/206pb, and 204pb/206pb ratios in phosphates for eet 87521agrain no. our in‐situ analyses using the sensitive high resolution ion microprobe (shrimp) installed at hiroshima university attain high sensitivity at high mass resolution of ∼5800 [sano et al. this in‐situ u/pb dating method has been successfully applied to extraterrestrial phosphates in some martian meteorites [sano et al.#### Ion microprobe U-Pb dating and REE analysis of apatite from

these features are similar to the previous report for the thin section #87521‐9 [warren and kallemeyn, 1989]. in contrast, low‐ti mare basalt samples are generally younger; they range in age from 3. thus, the previously reported ages of yamato 793274 and que 94281 are apparently different from those of eet 87521 (this work) and eet 96008 [anand et al. these young gas retention ages might have been affected by the shock event when the meteorite was launched to the earth.), which is determined as an intersection with the concordia line on the 238u/206pb ‐ 207pb/206pb plane. based on the available data of vlt basalts, nyquist et al.- Coolibri kleinanzeigen er sucht sie dusseldorf
#### Ion microprobe U-Pb dating of phosphates in lunar basaltic breccia

polnau and eugster [1998] reported a k‐ar age of 3770 ma for que 94281. here, it is noted that the observed pb/pb ratios are not affected by the matrix effect of mineral species. the areas of the grains selected for shrimp analysis were free from inclusions or cracks. this technique also allows for rapid analysis of small amounts of samples (even in thin sections), and will be useful for chronological studies of samples returned from the moon, mars and asteroids in the near future. comparison with other mare basalts[10] chronological studies of numerous samples of mare basalt and related pyroclastic deposits have been well documented (for summary, see nyquist and shih, 1992; nyquist et al. experimental details of the u‐pb analysis and the calibration of the data are given by sano et al.- Flirt und dating tipps fur frauen
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the pb/pb isochron ages of apatite (3530 ± 270 ma) and whitlockites (3519 ± 100 ma) for eet 96008 are consistent with those of eet 87521 (3503 ± 140 ma) presented here. [2001] have suggested that the formation age of vlt mare basalt for luna 24 is 3. ga based on the bulk concentration of 40ar and the k contents. for better understanding of the thermal history for these basaltic breccias containing some highland components, detailed investigations using in‐situ dating of phosphates, which are more resistant to secondary thermal processes, will be required in the future.[11] based on the similar launching ages in addition to many textural and mineralogical similarities, arai and warren [1999] and warren and ulff‐møller [1999] proposed that yamato 793274, yamato 981031, que 94281, eet 87521 and eet 96008, which are vlt mare basalt brecciated meteorites, were launched from the moon by a single impact event. although it remains unclear whether the relative sensitivity factor of u+/pb+ for whitlockite is the same as that for apatite, the upper intercept age of 3569 ± 100 ma for eet 96008 agrees well with 3531 ± 110 ma for eet 87521.

[12] in summary, ion microprobe u‐pb dating of phosphates in lunar basaltic breccia eet 87521 were successfully carried out., 2003], we also calculated a “total pb/u isochron age” from the linear regression line in the 238u/206pb‐207pb/206pb‐204pb/206pb 3d space [wendt, 1984, 1989; ludwig, 2001], assuming that the relative u+/pb+ sensitivity factor for whitlockite is the same as that for apatite and that the u‐pb systems are concordant. analyses of three whitlockites and five apatites give a 207pb/206pb age of 3503 ± 140 ma (95% confidence limit; mswd = 0. to old article view go to article navigation abstract[1] we report ion microprobe u‐pb dating of phosphates in lunar meteorite “elephant moraine 87521 (eet87521),” which is a fragmental breccia consisting of very‐low ti (vlt) basaltic clasts and a small component of highland‐derived materials. these fragments mainly consist of plagioclase and clinopyroxene including pigeonite. the observed u/pb and pb/pb ratios for eet 96008 were well presented by planar regression rather than linear regression in 238u/206pb ‐ 207pb/206pb ‐ 204pb/206pb 3d space, and the best‐fitted planar regression intercepts the concordia curve on the 238u/206pb ‐ 207pb/206pb plane at 3569 ± 100 ma and 100 ± 130 ma (2σ).

eet 87521 is a polymict fragmental breccia, although it is predominantly a single lithology (or a single group of closely‐related lithologies).. u/pb ages and systematics of eet 87521 and paired eet 96008[8] so far, the age of eet 87521 has not been well documented. the solid curve is an evolution line of the u‐pb system without initial lead (concordia line), and the line is the projected regression line onto the 238u/206pb ‐ 207pb/206pb plane. analysis of five apatites and three whitlockites indicate a total pb/u isochron age of 3531 ± 110 ma (95% confidence limit; mswd = 2. this suggests that the vlt basalt volcanism appears to have been prolonged on the moon.. sample and analytical methods[3] the eet 87521 sample used in this study was a polished thin section of #87521‐4, allocated by nasa‐jsc.

, 1999; eugster and terribilini, 1999], were also investigated by shrimp methods [anand et al. if this is the case, the chemical leaching of bulk samples to obtain an u‐pb age of yq‐meteorites might tend to lead to an “apparently” older age because the typical highland components often show older ages than those of typical mare basalts. the data for three whitlockites and five apatites are projected onto the 238u/206pb ‐ 207pb/206pb plane. observed 238u/206pb, 207pb/206pb and 204pb/206pb ratios of phosphates are listed in table 1. although the isotopic compositions of initial lead for the phosphates (206pb/204pb = 66 ± 99 and 207pb/204pb = 34 ± 81 at 95% confidence limit) can also be obtained from the intersection of the regression line with the 207pb/206pb‐204pb/206pb plane in the 3‐d correlation diagram, there are no additional constraints to the pb‐evolution model from these values because of the large uncertainties. apatite analyses alone give a 238u/206pb age of 4325 ± 930 ma (95% confidence limit; mswd = 0.

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ga, although some exceptions exist (the aluminous low‐ti mare basalts have ages of 3. [1996] reported a k‐ar age of 3300 ma (without analytical uncertainties), which is slightly younger than the eet 87521 phosphate formation of 3503 ± 140 ma found in this work. [1996] claimed that asuka 881757 should be classified into low‐ti mare basalt not into vlt because their bulk tio2 concentration ranges from 1.[9] the u‐pb systematics of phosphate in eet 96008, which is considered to be paired with eet 87521 [snyder et al. although the recent high‐precision thermal ionization mass spectrometry analyses enable the u‐pb dating from ∼10 microgram phosphates [e. ga for eet 87521 phosphates is distinct from vlt mare basalt for luna 24.